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MULTIPLE THERMAL GUT-OUT.

No. 413,703. Patented Oct. 29, 1889.

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No. 413,703. Patn'cedv Oct. 29, 1889.

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UNITED STATES PATENT OFFICE.

ALEXANDER VVURTS, OE PITTSBURG, PENNSYLVANIA, ASSIGNOR TO THE IVESTINGHOUSE ELECTRIC COMPANY, OF SAME PLACE.

MULTIPLE THERMAL CUT-OUT.

SPECIFICATION forming part of Letters Patent No. 413,703, dated October 29, 1889. Application fled June 21, 1889. Serial No. 315,119. (No model.)

To @ZZ whom t may concern.'

Be it knownthat I, ALEXANDER VVURTS, a citizen of the United States, residing in Pitts-A burg, county of Allegheny, and State of Penn sylvania, have invented a new and useful Improvement in Protecting Devices for Electric Circuits, (Case No, 328,) of which the following is a specification.

The invention relates to the class of inventions employed for automatically interrupting electrical circuit-connections upon the passage of currents of abnormal strength for the purpose of protecting the electrical apparatus connected in such circuits. It has been customary heretofore to interpose strips of fusible material in the circuits of dynamo-electric generators liable to be traversed by currents of abnormal strength, and these strips have been so constructed as to offer but little resist-ance to the current of normal strength, but to become heated and fused under the influence of currents of abnormal strength, thus interrupting the circuit-connections. It is found in practice that the fusible materials usually required for this purpose are such that when thus fused they form a vapor which acts as a conductor of electricity. An arc is thus formed across the space intervening between the ends of the fused strip, and the current developed by the dynamo then continues to flow across the space.

The object of my invention is to prevent the occurrence of such an arc and to insure that a current of sufficient strength to fuse the strip will cause a complete interruption of the circuit.

The invention consists in forming a shuntcircuit around the fusible strip so constructed as to receive the entire current immediately upon the destruction of the fusible strip, and then itself become interrupted in such a manner as to form an opening of the circuit.

In carrying the invention into practice a second fusible strip may be connected in the shuntcircuit, and this is of such material and so proportioned as to be brought into action immediately after the first striphas been destroyed, but to convey the current for a sufficient period to prevent it from bridging the space between the fused ends of the first strip. The second or shunt fuse may consist of one or more strips of German silver or iron or other material which does not readily establish an are when melted. In practice German silver is found to serve the purpose exceedingly well. Iron also is found to oper ate very successfully on account of its tendency to separate into globules when heated to a high temperature, and thus avoid the formation of an arc.

In the accompanying drawings, Figure l is a side elevation of a fusible cut-out embodying the invention. Fig. 2 is a plan of the same, and Fig. 8 is a diagram of a system of. circuits supplied with the safety devices.

Referring tov the figures, A represents a dynamo-electric generator or other suitable source of electric currents, and IV represents va work-circuit supplied with currents from the lines L L2, leading from the poles of the generator to the work-circuit- In one or both of the two lines L L2 there is inserted a safety fusible device. These devices are constructed as more particularly shown in Figs. l and 2. They consist of a strip B, of some suitable welli known fusible compound or metal-such as lead, for instanceand a shuntecircuit througha fusible wire or strip Z). This latter may with advantage be of German silver and of greater resistance than the strip B', so that normally it conveys but a comparatively small proportion of the current. The strip B is shown as held in binding-plates b and b2, which also carry arms d d2, of conducting material, supporting the strip b. In the drawings a second strip B2 is shown as placed upon the same supporting-block D, the design being to use the second as areserve in case the first is destroyed. A switch-plug e is employed for connecting the two plates b2. By connecting the lines with the plate b of the strip B and the plate U2 of the strip B2 the strip B will be connected in circuit. By placing the switch-plug e between the other two plates b the strip 1)2 will be placed in circuit. This is a convenient form of device to employ; but it will be evident that the invention is equally applicable to other forms of devices. f

The strip l) may be constructed of one or more strands of German-silver wire or strips of iron or other suitable material. 'lhe relative IOO conductivities of the two fusible strips thus connected in shunt upon each other are such that each will conduct its -proportion of the normal current of the circuit without fusing or becoming overheated. If,'however, a current of excessive strength-such as a stroke of lightning, for instance-should traverse the main line, then the increase of the current flowing through the strip Bv Would be sufiicient to cause it to fuse, whereupon the circuit would remain complete through the strip b alone. The presence of this circuit, however, would preventthe formation of an arc between the terminals of the safety-strip B',

' but the increase of current compelled to traverce the shunt-circuit would immediately fuse the strip b. This strip, however, is of such construction or formation as to prevent the establishment of an arc. It simply serves to entirely interrupt the circuit-connections by being suddenly fused or exploded under the influence of the entire current.

I claim as my invention- 1. An interrupting device for electric circuits, consisting ot' the combination, With a fusible strip, of a normally-closed shunt-circuit around the same, and a second fusible strip of conducting material through which the connections of said normally-closed shuntcircuit are completed, said second strip having a greater resistance than the first-named strip and serving to permanently interrupt the shunt-circuit connections when the firstnamed fuse has been destroyed.

2. An interrupting device for electric circuits, consisting of the combination, with a fusible strip, of a normally-'closed shunt-circuit around the same, and a second fusible strip of conducting material through which the connections of said normally-closed shuntcircuit are completed, said second strip being of a different material from the first-named strip and serving to permanently interrupt the shunt-circuit rconnections when the firstnamed fuse has been destroyed.

3. An interrupting device for electric circuits, consisting of the combination, with an electric circuit; of afusible strip, a normallyclosed shunt-ciredit, and a second fusible strip of conducting material through which the connections of the said normally-closed shunt-circuit are completed, said strips being so proportioned to each other and to the circuit that an abnormal increase of current in the circuit will destroy the firstnamed strip,

While the second will be destroyed by the resultant current traversing its circuit, thereby permanently interrupting both'circuits.

In testimony Whereofl have hereunto subscribed my name this 14th day of June, A. D. 1889.

W. D. UPTEGRAFF,. CHARLES A. TERRY. 

